ᐅ Types of Screed in Anhydrite and Cement-Based Flooring

Hello everyone,
this year we will be building a single-family house with approximately 200 m² (2,150 sq ft) of living space. The underfloor heating (air-to-water heat pump) is installed within the screed. The topic of screed is still quite unclear to me and it keeps occupying my mind. From research within this forum, many questions have already been raised and some qualified answers given, but the actual pros and cons are still not entirely clear to me (by the way, every company I ask says something different :-))

I will summarize my modest knowledge so far:
Cement screed (flowing screed):
Positive: water resistance
Negative: prone to cracking, prone to curling, somewhat more expensive, joints required on large surfaces

Cement screed (site-applied screed, smoothed):
Positive: water resistance, less water and therefore shorter drying time, less prone to curling
Negative: cracking risk?, much more expensive than anhydrite or flowing cement screed

Anhydrite screed:
Positive: no joints required on large surfaces, fairly inexpensive
Negative: water resistance

Question: How do these options behave in relation to the built-in underfloor heating? Anhydrite screed is often marketed as "heating screed." Is its performance really that much better than cement screed?
The interior finishing will be done entirely with drywall (gypsum plasterboards). Is my concern about the high moisture content with flowing screed justified (since gypsum plasterboards are known to absorb moisture) or is this negligible?

Considerations: Basically, I was leaning toward using fully cement screed (flowing screed) because it is self-leveling. However, I keep hearing concerns about curling and similar issues. The alternative of using the more labor-intensive and “drier” site-applied screed (smoothed) is reportedly quite expensive (but we have not received an offer yet).
Initially, anhydrite screed was not even considered, but the feature of being “joint-free” (kitchen, living, dining area is about 50 m² (540 sq ft)) makes it fundamentally interesting. My real concern here is the issue of water resistance.

I look forward to your experiences or suggestions.

Thank you
Sebastian

Sebastian82 schrieb:

Question: How do the different types compare regarding underfloor heating installation?

So that you won’t notice any difference.

In terms of cost, the order is usually cement screed, cement flowing screed, and anhydrite screed (calcium sulfate screed).

Sebastian82 schrieb:

The interior finishing will be done entirely as drywall (gypsum board). Is my concern about the high moisture with flowing screed justified (gypsum boards are known to absorb moisture easily), or is it negligible?

It’s negligible. All screeds contain a significant amount of moisture. You’ll have to wait anyway before starting the interior finishing.

Sebastian82 schrieb:

Anhydrite wasn’t initially an option, but with the topic of seamless surfaces (kitchen, living, and dining area adding up to around 50 m² (540 sq ft)), it’s basically interesting. My real concern is about water resistance.

Whether seamless is possible is something your screed installer can tell you.
Regarding water resistance, you have to ask yourself how often you actually spill hundreds of liters of water on your floors. If a bucket tips over once, you’ll clean it up and that’s it. The issue concerns large amounts of water penetrating the screed. This usually only matters in bathrooms or in the event of a real water damage, for example, from a broken water pipe.

Screed work is really the easiest trade; it doesn’t matter what you do. It’s all basically the same stuff 🙂

Anhydrite screed in wet areas is sealed, and this completes the matter.

Thank you for the quick initial feedback.

@nordanney: Does your price list go from expensive to cheap? (at least that’s what I assume)

The issue of water resistance is not so easy for me to answer. Of course, something needs to happen for water to reach the screed. However, with a water-based underfloor heating system, I’m already exposed to a risk of water damage from all the connections (not to mention the dangers of leaking pipes). I have the same risk with cement screed, but supposedly it can be professionally dried. Or am I being too cautious?

What do you think about the option of using anhydrite screed in the living areas and cement screed in the bathroom? (The tiler has to level the walk-in shower anyway, so could they then handle the bathroom as well?) Is this practical?

Sebastian82 schrieb:

@nordanney: Your price ranking goes from expensive to cheap? (at least that’s what I assume)

The other way around, from cheap to expensive.

Sebastian82 schrieb:

Or am I being too critical?

Yes.
Calcium sulfate screed is state of the art. Leaky pipes are almost impossible, since each circuit consists of one continuous pipe (no joining). The connections are not any more “leaky” than any other connections.

Sebastian82 schrieb:

What do you think about the option of using anhydrite in living areas and cement screed in the bathroom (the tiler has to level the walk-in shower anyway and could basically do the whole bathroom then? Practical?

Sort of. The tiler should properly prepare the shower area, including drainage. That is usually not done by the screed installers. However, the tiler won’t apply the screed to the entire bathroom. There is no reason not to use calcium sulfate screed in the bathroom as well, followed by proper waterproofing. Full waterproofing is highly recommended even with “standard” screed.